Thermal relay



NOV. 17, 1942. $T|M5QN 2,302,399

THERMAL RELAY Filed Feb. 15, 1942 Fjg. I.

Inventor: Allen 6. Stimson,

yfwyf M4 His Atborngg.

rmaduov. 11,1942

THERMAL RELAY Allen G. Stimson, Lynnfleld, Mass., assignor to GeneralElectric Company, a corporation or New York Application February 13,1942, Serial No. 430,784

15 Claims.

, structure and are subject to the disadvantage of high cost.

Accordingly, it is an object of my invention to provide a thermal relaywhich shall be emcient and reliable in operation and simpleandinexpensive to manufacture in quantity.

It is a further object of my invention to provide a thermal relay havingrelatively long time delay in operation and capable of exerting arelatively large force over a wide range of movement.

It is a still further object of my invention to provide an ambienttemperature compensated thermal relay which shall operate to increasethe pressure of normally closed contacts immediately prior to separationof the contacts.

It is a specific object of my invention to provide a thermal time delaystarting for electric discharge lamps which shall operate efllcientlyand which shall be simple and inexpensive to manuiacture.

My relay comprises essentially a pair of movable bimetallic membersdisposed in parallel spaced relation and connected together at one end.The other end of one of the members is fixed to the base, the adjacentend of the other bimetallic member being free and carrying a movableswitch contact. Upon unequal heating of the bimetal members they willdeflect unequally so that the free end of the member carrying themovable contact will move relative to the juxtaposed fixed end of theother member. On the other hand, if the members are equally heated orcooled, as by a change in the ambient temperature, they will deflectsynchronously so that there will be no relative movement between thefixed end of the one member and the juxtaposed iree contact carrying endof the other member.

My invention will be better understood by referring now to the followingdetailed description taken in conjunction with the accompanying drawing,in which Fig. 1 is a schematic perspec- 55 tive view of a relayembodying one form of my invention and connected in circuit with anelectric discharge lamp; Fig. 2 is a side elevation of the relay in itsdeflected position immediately before tripping; and Fig. 3 is a sideview of the relay in its position of deflection immediately aftertripping.

In the drawing I have represented at iii an electric discharge lampsuch, for example, as the sodium vapor lamp, having at the ends thereofthe anodes II and H and the filamentary cathodes IZ and I3, each cathodebeing connected at one end with the adjacent anode and at the other endwith one of the lamp terminals by which the energy is supplied to thelamp. The source of energy supply is represented at H as being analternating current circuit of the constant current type such as iscommonly used in series lighting systems. Energy is shown taken from thecircuit It by means of a series transformer I5 between the ends of thesecondary of which and the lamp I have shown the usual film cutout Hi,the radio frequency capacitor 11 and the radio frequency choke l8.

In order that the lamp cathodes may be heated to the desired temperatureand suitably activated before the discharge starts in the lamp I connectthem at starting by a low resistance circuit for a predetermined timeafter which the circuit is automatically opened and the dischargestarts. For this purpose I have provided a thermal relay comprising apair of switch contacts 19 and 20 and an operating element in the formof a sinuous bimetallic member 25. The fixed contact I9 is mounted upona base member of the relay indicated at 26 and the movable contact 20 iscarried at the end of a resilient cantilever spring strip 21 which isattached to and extends from the connected free ends of an inner pair ofmovable leg portions of the bimetallic element 25.

The bimetallic operating member 25 comprises a juxtaposed pair of innerleg portions 28, 29 and a pair of outer leg portions 30, 3|. The legportions are disposed in edge-to-edge parallel spaced relation and areconnected together at alternate juxtaposed ends to form a sinuouscurrent path through all the legs in series circuit relation. The innerbimetallic members 28 and 29 are of substantially the same length as theouter members 30 and 3| but are of considerably smaller crosssectionalarea. Hence, each inner leg member 28, 29 has a greater electricalresistance and a smaller heat dissipating capacity than each outer legmember 30, 3|. The bimetallic element 25 may easily be fabricated froman E-shaped punching by slotting the central leg of the punchinglongitudinally for substantially its entire length, the slot fallingsomewhat short of the free end of the center leg, thereby to form ineilect a pair of juxtaposed U-shaped bimetallic members connectedtogether at the free ends of their parallelly disposed smaller innerlegs. The bimetal 25 is supported upon the relay base at the extremitiesof the relatively large outer legs. As shown, the extremities of theouter leg portions 38 and 3| are rigidly connected to terminalconductors 32 and 33 which form part of the relay base. The bimetallicmember 25 is arranged so that in its unheated position the contacts l9and 28' assume a normally closed position. The contacts are further heldin this position and are provided with a snap action in operation byproviding at the free ends of the inner leg portions 28 and 29 amagnetizable keeper 34 disposed for operation in conjunction with asmall permanent magnet 35 mounted upon the relay base.

In the form of my invention shown by way of illustration in the drawingthe bimetallic element 25 is permanently connected in series circuitrelation with the discharge lamp I8. In operation, when energy issupplied to the circuit M an alternating current passes through thesinuous bimetallic element 25 in series circuit relation with thefilamentary cathodes i2 and I3 and the anode short circuiting relaycontacts [9 and 28. The inner and outer legs of the bimetallic element25 are heated by the current passing through them, so that the lower endof the element 25 moves to the right, and away from the relay base, asviewed in the drawing, as the entire element assumes a curved shape. Dueto the fact that the inner legs 28 and 29 are of higher resistance thanthe outer legs 38 and 3i and due also to the fact that the inner legshave a smaller heat dissipating capacity than the outer legs, the innerand outer legs are unequally heated and the inner legs will attain atemperature higher than that of the outer legs. Be-

cause of the higher temperature of the inner legs these legs will tendto curl to a greater extent than the outer legs 38 and 3!. The tendencyof the inner legs 28 and 29 to deflect to a greater extent than theouter legs is initially restrained by the snap action magnet 35 and itskeeper 34. tion before the central leg portions 28 and 29 have built upby their higher temperature suflicient internal stress to pull thekeeper 34 away from the magnet 35 both the inner and outer leg portionsare constrained to deflect in a substantially synchronous manner, sincethe upper ends of the outer leg members are fixed to the base and theupper end of the inner leg members is magnetically held in substantiallyits initial position while the lower ends of the inner and outer legmembers are firmly connected together During this initial period ofdefiecby transverse portions of the bimetal. The position of thebimetallic member immediately before opening of the contacts is shown atFig. 2. It is important to note that during the initial period ofsubstantially synchronous deflection of the inner and outer legs themovement of the lower end of the bimetal 25 away from the relay basecauses the free end of the inner legs 28 and 29 to pivot about the upperend of the magnet keeper 34, as shown at Fig. 2. This pivotal movementtends to pull the lower end of the magnet keeper 3| away from the magnetbut does not of itself sumciently diminish the magnetic force to permitthe center leg portions 28 and 23 to snap to their open circuitpositions. It is evident that the pivotal movement Just described willincrease the contact pressure between the fixedcontact l9 and themovable contact 28. When finally the inequality in the heating of theinner and outer leg portions of the bimetallic element 25 has attained apredetermined degree the internal strain built up in the inner legportions 28 and 29 tending to deflect these leg portions farther thanthe outer leg portions 38 and 3! will be suflicient to pull the keeper34 away from the magnet 35 and thereby separate the relay contacts l9and 28 with a snap action. The position of the bimetallic memberimmediately after separation of the contacts is shown at Fig. 3.Separation of the relay contacts initiates a discharge current in thelamp I8 by removing the short circuit across the anodes H and II.

Ambient temperature compensation of my thermal relay is inherent due tothe fact that the movable contact 28 is mounted at the same end of thebimetallic member 25 at which attachment of the bimetallic member to therelay base is made. Thus, under changing ambient temperature conditions,the inner and outer legs of the bimetal 25 are equally heated anddeflect equally so that the free end of the inner leg portions 28 and 29to which the movable contact 28 is attached does not move with respectto the extremities of the outer leg portions 38 and 32 which areattached to the relay base.

By reason of the construction of the bimetallic device which I haveprovided the time delay between its energization and its movement toopen circuit position is suiiicient to permit the cathodes l2 and i3 tobecome heated to the desired temperature and thus to become activated.This time delay may be of the order of 25 to 45 seconds. A bimetallicmember of the configuration which I have provided is particularlyadapted to applications requiring such a relatively long time delay andalso provides a substantial operating force eifective over a wide rangeof movement.

While for convenience of fabrication I prefer to form my bimetallicelement 25 from an E- shaped punching having three legs of substantiallythe same size so that when the center leg is slotted it forms twocentral leg portions having both a higher electrical resistance and alower dissipating capacity than the outer legs, it will be understood bythose skilled in the art that it is in the scope of my invention toprovide a, sinuous bimetallic member in which any desired means isprovided for unequally heating a pair of parallelly-disposed connectedleg portions. For example, this may be eflected by supplying to both legportions equal amounts of heat but constructing the leg portions to havedissimilar heat dissipating characteristics. On the other hand, the sameeil'ect may be obtained by providing leg portions havingsimilar heattransfer characteristics but to which unlike quantities of spect to theinner leg portion the greater will be the transfer of heat from theinner leg to the outer leg and hence, the greater will be the time delaybefore the inner leg assumes a sufficiently high temperature to assumeits independent open circuit position of greater deflection with respectto the outer leg,

While I have shown only one preferred embodiment of my invention by wayof illustration, many other modifications will occur to those skilled inthe art and I wish to have it understood that I intend by the appendedclaims to cover all such modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent 01 the UnitedStates is:

1. A thermal relay comprising a base, a fixed contact mounted upon saidbase, a pair of thermal responsive movable members in parallel spacedrelation, one of said thermal responsive members being mounted at oneend upon said base and having its other end connected to the juxtaposedend of the other of said thermal responsive members, a movable contactmounted upon the free end of said other thermal responsive member forcooperation with said fixed contact, means for unequally heating saidthermal responsive members to separate said contacts, and snap actingmeans operable in conjunction with said free end of said other thermalresponsive member releasably to retain said contacts in engagement.

2. A compensated thermal relay comprising a base, a fixed contactmounted upon said base, a pair of thermal responsive movable members inparallel spaced relation, said thermal responsive members being arrangedfor deflection in the same direction upon similar changes in temperaturethereof and one of said members being mounted at one end upon said baseand having its other end connected to the juxtaposed end of the other ofsaid thermal responsive members, a movable contact mounted upon the freeend of said other thermal responsive member for cooperation with saidfixed contact, means for unequally heating said thermal responsivemembers to separate said contacts, and snap acting means operable inconjunction with said free end of said other thermal responsive memberreleasably to retain said contacts in engagement.

3. A compensated thermal relay comprising a base, a fixed contactmounted upon said base, a pair of thermal current responsive movablemembers in parallel spaced relation, one of said current responsivemembers being mounted at one end upon said base and having its other endmechanically and electrically connected to the juxtaposed end of theother of said current responsive members, said current responsivemembers having dissimilar thermal transfer characteristics and beingarranged to deflect in the same direction upon the application of heatthereto, a movable contact mounted upon the free end of said othercurrent responsive member for cooperation with said fixed contact, meansfor supplying substantially equal heating currents to said currentresponsive members thereby unequally to heat said members and toseparate said contacts, and snap acting means for releasably retainingsaid contacts in engagement.

4. A compensated thermal relay comprising a base, a fixed contactmounted upon said base, a pair of thermal current responsive movablemembers in parallel spaced relation one of said current responsivemembers being mounted at one end upon said base and having its other endmechanically and electrically connected to the juxtaposed end of theother of said current responsive members, said current responsivemembers having substantially the same length but being of dissimilarelectrical resistance, a movable contact mounted upon the free end ofsaid other current responsive member for cooperation with said fixedcontact, means for supplying substantially similar heating current tosaid current responsive members thereby unequally to heat said membersand to separate said contacts, and snap acting means for releasablyretaining said contacts in engagement.

5. A thermal relay comprising a base, fixed and movable switch contacts,a U-shaped movable member having two thermal responsive leg portionsarranged for deflection in the same direction upon similar changes inthe temperature thereof, the free end of one of said leg portionscarrying said movable contact and the juxtaposed end of the other ofsaid leg portions being fixedly attached to said base, means forunequally heating said leg portions to separate said contacts. and snapacting means for releasably retaining said contacts in engagement.

6. A compensated thermal relay comprising a base, a fixed contactmounted upon said base, a U-shaped bimetallic movable member having twoleg portions of dissimilar cross sectional areas, a movable contactmounted at the free end of one of said leg portions for cooperation withsaid fixed contact, means for rigidly attaching the juxtaposed end ofthe other leg portion to said base, means for supplying a heatingcurrent to said bimetallic movable member with said leg portionsconnected in series circuit relation thereby unequally to heat said legportions and to separate said contacts, and snap acting means operablein conjunction with said free end of said one leg portion for releasablyretaining said contacts in engagement.

'7, A compensated thermal relay comprising a base, a fixed contactmounted upon said base, a U-shaped bimetallic movable element comprisinga pair of leg portions of substantially equal length lying inedge-to-edge parallel spaced relation, said leg portions havingdissimilar cross-sectional areas and being electrically connected in,series circuit relation, a movable contact mounted upon the free end ofone of said leg portions for cooperation with said fixed contact, meansfor rigidly connecting the juxtaposed end of the other of said legportions to said base, means for supplying a heating current to saidU-shaped bimetallic element thereby unequally to heat said leg portionand to separate said contacts, and snap acting means operable inconjunction with the end of said other leg portion releasably to retainsaid contacts in engagement.

8. A compensated thermal relay comprising a base, a fixed contactmounted upon said base, a pair of bimetallic'members disposed inparallel spaced relation, a first of said bimetallic members beingmounted at one end upon said base and having its other end mechanicallyand elecirically connected to the juxtaposed end of the second of saidbimetallic members, said bimetallic members being of substantially thesame length but of dissimilar cross-sectional areas and being disposedto deflect in the same direction upon the application of heat thereto, aresilient contact spring extending from the free end of said secondbimetallic member and carrying at its end a movable contact forcooperation with said fixed contacts, means for supplyin a heatingcurrent to said bimetallic members in series circuit relation therebyunequally to heat said members and to separate said contacts, and snapacting means engaging said free end of said second bimetallic memberreleasably to retain said-contacts in engagements and to increase thecontact pressure prior to their separation.

9. A compensated thermal relay comprising a base, a fixed contactmounted upon said base, a lJ-shaped thermal responsive bimetallicelement comprising a pair oi leg portions of substantially equal lengthlying in edge-to-edge parallel spaced relation, said leg portions havingdissimilar cross-sectional areas and being electrically connected inseries circuit relation, a resilient contact spring connected to andextending from the free end of one of said leg portions and carrying atits end a movable contact disposed normally to engage said fixedcontact, supporting means for rigidly connecting the juxtaposed end ofthe other of said leg portions to said base, a magnet mounted upon saidbase adjacent said free end of said one leg portion, a keeper ior saidmagnet connected to said free end of said one leg portion, means for supplying a heating current to said U-shaped blmetallic element forunequally heating said leg portions thereby to produce unequaldeflections of said portions and to separate said contacts, said magnetreleasably retaining said keeper in engagement therewith over a portionof the heating period and constraining said one leg portion to pivotabout its free end thereby to increase the contact pressure prior to theseparation of said contacts.

10. A thermal relay comprising a base, a fixed contact mounted upon saidbase, a bimetallic element of sinuous configuration comprising aninterconnected pair of inner legs and a juxtaposed pair of outer legsconnected to said inner legs, said pairs of legs being disposed in substantially edge-to-edge parallel spaced relation, a movable contactmounted upon the interconnected ends of said inner legs for cooperationwith said fixed contact, supporting means for connecting the juxtaposedends of said outer legs to said base, means for unequally heating saidinner and outer legs to separate said contacts, and snap acting meansoperable in conjunction with the free end of said inner legs releasablyto retain said contacts in engagement.

11. A. thermal relay comprising a base, a fixed contact mounted uponsaid base, a bimetallic element of sinuous configuration comprising aninterconnected pair of inner legs of relatively small cross section anda juxtaposed pair of outer legs connected to said inner legs and havinga relatively large cross section, said pairs of legs being disposed insubstantially edge-to-edge parallel spaced relation, means for mountingsaid bimetallic element upon said base at the ends of said outer legslying adjacent the interconnected ends of said inner legs, saidinterconnected ends carrying a movable contact for cooperation with saidfixed contact, means for supplying a heating current to said bimetallicelement, said heating current passing through said legs in seriescircuit relation thereby unequally to heat said inner and outer pairs oflegs, the unequal heating of said pairs of legs tending to produce agreater deflection of said inner legs than of said outer legs and toseparate said contacts,

and magnetic means mounted upon the free ends aa oaaco of said innerlegs releasably to constrain both said pairs of less to substantiallysynchronous deflection during an initial portion oi their movement andthereafter to release said inner legs with a snap action for movement toan open circuit position.

12. A compensated thermal relay comprising a base, a fixed contactmounted upon said bas a bimetallic element of sinuous configurationcomprising an interconnected pair of inner legs and a juxtaposed pair ofouter legs connected to said inner legs, said legs being disposed insubstantially edge-to-edge parallel spaced relation and said pairs oflegs having dissimilar crosssectional areas, a resilient contact springconnected to and extending from the interconnected ends of said innerlegs and carrying at its end a movable contact disposed normally toengage said fixed contact, supporting means for rigidly connecting thejuxtaposed ends of said outer legs to said base, a magnetic keepermounted upon said interconnected ends of said inner legs, a

magnet mounted upon said base adjacent said keeper releasably torestrain movement of said inner legs, means for supplying a heatingcurrent to said bimetallic element traversing said legs in seriescircuit relation, said heating current unequally heating said inner andouter legs thereby to produce unequal deflections thereof to separatesaid contacts, said magnet releasably retaining said keeper inengagement therewith over an initial portion of the heating period andconstraining said inner and outer legs to defiect substantiallysynchronously during said initial period while said inner legs pivotupon said keeper thereby to increase the contact pressure prior to theseparation of said contacts.

13. A thermal relay comprising a base, a fixed contact mounted upon saidbase, a U-shaped bimetallic member having a pair of leg portions inparallel spaced relation, said bimetallic member being mounted upon saidbase at the extremity of one 'of said leg portions and carrying amovable contact at the free end of the other of said leg portions, saidmovable contact being disposed to engage said fixed contact in theunheated positlon of said bimetallic member, means for unequally heatingsaid leg portions to separate said contacts, and magnetic means operablein conjunction with said free end of said leg portion initially toconstrain said leg portions to deflect synchronously and subsequently topermit said contacts to separate with a snap action.

14. A thermal relay comprising a base, a fixed contact mounted upon saidbase, a pair of thermal responsive movable members in parallel spacedrelation, one of said thermal responsive members being mounted at oneend upon said base and having its other end connected to the juxtaposedend of the other of said thermal responsive members, a movable contactmounted upon the free end of said other thermal responsive member forcooperation with said fixed contact, and means for unequally heatingsaid thermal responsive members to separate said contacts.

15. A compensated thermal relay comprising a base, a fixed contactmounted upon said base, a pair of thermal current responsive movablemembers in parallel spaced relation, one of said current responsivemembers being mounted at one end upon said base and having its other endmechanically and electrically connected to for cooperation with saidfixed contact, and means for supplying substantially equal heatingcurrents to said current responsive members thereby unequally to heatsaid members and to 5 separate said contacts.

ALLEN G. STDESON.

